The present invention relates to a damper disc employed in a friction clutch for an automobile and others, and more particularly, to a friction mechanism in such a damper disc.
In order to improve a torsion angle and others of a disc, the applicant has already developed a disc as shown in FIG. 1 in a Japanese Patent Application No. 56-20510 (Laid-open publication No. 57-134019). Referring to FIG. 1, which is a sectional view, a hub 2 splined to an output shaft 1 (only a center line thereof is illustrated) is provided with radial flange part 3. A pair of side plates 5 and disposed at respective sides of the flange part 3. A friction facing 7 is connected through cushioning plates 6 to one of the side plates 5. The flange part 3 is divided into a radially inner flange 8 and a radially outer flange 9. The outer flange 9 engages with the outer periphery of the inner flange 8 and is connected to the flange 8 through a weak spring 12 so that both flanges 8 and 9 may be twistable with respect to each other. The flange 9 and the side plates 5 have openings 13 and 14, respectively, in which torsion springs 15 are disposed for twistably connecting the side plates 5 and the flange 9 together.
Sub-plate 16 are fixed at respective surfaces of the flange 9. Radially inner portions of the sub-plates 16 are extended to both sides of the inner flange 8 to hold the spring 12. Wave springs 20 are interposed between the inner peripheral portions of the sub-plates 16 and the flange 8. Friction washers 21 are interposed between the sub-plates 16 and the side plates 5, respectively.
In the above disc, a torque transmitted from the facing 7 to the side plates 5 is transmitted through the springs 15, flange 9 and spring 12 to the flange 8, hub 2 and output shaft 1. In this operation, while the torque is small, which is a first torsion operation, the flange 9 is untwistably connected to the side plates 5 and twists or torsionally turns with respect to the flange 8 while compressing the spring 12. When the torque increases over a predetermined value, which is a second torsion operation, the flange 9 is untwistably connected to the flange 8, and the side plates 5 twist or torsionally turn with respect to the flanges 8 and 9. In accordance with this twisting operation, sliding occurs on the surfaces of the springs 20 and the washers 21, so that hysteresis torque is generated in the damping characteristic by frictional forces corresponding to above sliding. The sliding on the wave springs 20 occurs in the first torsion operation, and the sliding on the friction washers 21 occurs in the second torsion operation. Therefore, the frictional forces on the wave springs 20 and on the friction washers 21 are generally determined to be different to each other, so that the hysteresis torque may change in two steps for effectively absorbing torque vibration throughout the torsion area.
However, in above known structure, all of the friction members, which are the springs 20 and washers 21, are disposed to axially overlap each other with the flange 8 and sub-plates 16 therebetween. Therefore, when the friction washers 21 are worn and become thin after a long use, the springs 20 axially extend, so that the pressure between the springs 20, flange 8 and the sub-plates 16 decreases. As a result the biasing force of the springs 20 against the washers 21 as well as the pressure on the washers 21 also decreases. Consequently, the frictional forces on the springs 20 and the washers 21 change and the hysteresis torque becomes unstable. Thus, the intended absorbing effect for the torque vibration can not be obtained.
The above problem is caused not only in the friction mechanism in FIG. 1 including the springs 20 and the washers 21 but also in the mechanisms in FIGS. 2 to 5.
In the mechanism in FIG. 2, a conical spring 22 and two friction members 23 (such as a friction washer and a friction plate) are interposed between the right (in FIG. 2) side plates 5 and the sub-plate 16. A conical spring 22 is also interposed between the left sub-plate 16 and the flange 8. In the mechanism in FIG. 3, a wave spring 20 and a conical spring 22 are used as spring means. In the mechanism in FIG. 4, a conical spring 22 is interposed together with a friction members 23 between the left side plate 5 and the sub-plate 16, and a conical spring 22 is interposed also between the right sub-plate 16 and the flange 8. In the disc in FIG. 5, a flange part 3 is not divided and has an integral structure, and wave springs 20 are disposed at respective sides of the flange part 3.
In the discs in FIGS. 2 to 5, all of the frictional members (20, 22, 23) are disposed to axially overlap each other. Therefore, they have same problem as that in FIG. 1.
Accordingly, it is an object of the invention to provide an improved structure, overcoming the above-noted problems, wherein a first friction means for a first torsion operation and a second friction means for a second torsion operation are disposed independently of each other.
According to the invention, a friction mechanism in a damper disc comprises a cylindrical hub adapted to connect to an output means and having a radial flange; a pair of side plates connected to an input member and disposed at respective sides of the flange; a sub-plate disposed between the side plate and the flange; a torsion spring twistably connecting the flange and the side plates together; a first friction device for a first torsion operation; and a second friction device for a second torsion operation; said sub-plates being adapted to torsionally turn with respect to one of the flange and the side plates in a first torsion operation and to torsionally turn with respect to the other of the flange and the side plates in a second torsion operation; and said first and second friction devices are radially shifted to each other and are disposed independently of each other.
Other and further objects, features and advantages of the invention will appear more fully from the following description of the preferred embodiments of the invention.